A cooled gas turbine blade with sheet metal-form impingement cooling inserts is known from JP 2001-14 06 02-A. An impingement cooling insert, triangular-shaped in cross section, installed in the region of the blade trailing edge of the turbine blade, is spaced away from the inner surface of the outer wall and provided with impingement cooling holes. During the operation of the gas turbine, the cavity enclosed by the impingement cooling insert is fed with cooling air, which then exits through the impingement cooling holes and impinges upon the inner surface of the externally hotly flow-washed outer wall, in order to cool the latter.
Moreover, U.S. Pat. No. 6,439,847 discloses a turbine blade with an insert of a form-memory alloy which for the improvement of the cooling of the turbine blade increases the volume of a cooling system by contraction after the exceeding of a threshold temperature. The insert, changing in its cross-sectional shape, has two overlapping sheet metal ends, which are displaceable parallel to the flow direction of a hot gas. In an alternative development, U.S. Pat. No. 6,439,847 shows, moreover, a wave-like insert of a form-memory alloy.
In addition, it is known that impingement cooling inserts comprise two separate parts which are inserted one after the other into the cavity of a turbine blade. The first part is fixed gastight on the radially inner platform and the second part is fixed gastight on the radially outer platform in order to avoid losses in the feed region. As a result, the two parts lie one upon the other in an overlapping flat sliding seat to enable a relative movement during the operation of the gas turbine.
During cold start or during transient operation of the gas turbine, different thermal expansions take place in the gas turbine blade, especially in the hotly flow-washed outer wall and in the cooler impingement cooling insert which is not yet completely heated or unevenly heated. These, especially expansions occurring in the direction of the blade axis, can mechanically relieve the overlap area or the sliding seat respectively and so enable an unwanted gap between the two abutting sections of the impingement cooling element through which cooling air can escape from the inside of the impingement cooling insert, unused as leakage.